1. Field of the Invention
This invention pertains generally to the field of automatic milking machines, and particularly to stimulating systems for automatically stimulating milk let-down in a cow.
2. Description of the Prior Art
Proper milking procedures require that the cow be stimulated prior to the initiation of milking in order to cause the milk in the udder to "let-down". The milk in the upper structure of the udder is contained in so-called alveoli, small cell-like structures surrounded by muscle tissue. Proper stimulation of the udder apparently provides a neurological signal which causes release of a substance known as oxytocin into the blood stream of the cow. The oxytocin has the effect of stimulating the muscle tissue surrounding the alveoli and causing them to contract to force the milk out.
Milk let-down on a cow can be stimulated by a number of events, especially those which are associated by the cow with milking time. In automatic milking operations, the stimulation is commonly accomplished by spraying or washing the udder with warm water, hand massaging the udder for a few seconds or stripping for milk.
Unpublished research from the University of Leipzig in Germany indicates that maximum generation of oxytocin, and resulting maximum let-down of milk, is obtained by forcefully squeezing all teats for at least approximately 60 seconds. It is assumed that the resulting increase in milk production from this type of stimulation is due to greater amounts of oxytocin being released at approximately the same time, which causes immediate and full let-down in the cow. Using this procedure, the University of Leipzig reported a moderate increase in production for the first lactation after instituting the stimulation procedure. Greater increases were found in the second half of the first lactation and in the second lactation. It is believed that with this type of stimulation, the cow not only injects oxytocin into the blood stream, but also small amounts of a hormone called prolactin. This second hormone is not entirely understood but is believed to have some connection to the development of the udder. Stimulation in this manner over a period of time thus appears to result in an increase in the mass of alveoli producing milk, and therefore increased milk production in the second lactation as reported.
Stimulation procedures that depend on the actions of the operator, such as hand stripping of the teats or washing of the udder, are unreliable because the operator may change his actions from day to day. Stimulating procedures which wet the udder can also be undesirable where the cow immediately leaves the milking barn with a wet udder and can be exposed to cold weather.